Butt joints (again)

How good is good enough? As some will remember, I'm finishing my basement. I'm finishing the drywall now. I have built hot rods all my adult life and I tend to try to get the walls straight enough to paint gloss black. Needless to say it works me to death. The recessed joints aren't a problem. But the butt joints are killing me. I'm currently mudding out 18 inches or so either side of the butt joints. I sand them and feather them out, but when I feel them I can still detect the raised area. I used mesh tape and I sanded the first coat till I could just begin to see the mesh in an effort to keep the center as low as possible. Then on the second coat I skimmed over it very lightly. Assuming I'm actually sanding the compound flat from the center out in both directions, how wide should the feather be to keep the rise in the surface from being noticeable? Thanks

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Butt joints (again)

My butts are 36 inches wide. I use a flat 18" trowel on both sides after my tape is semi dry then on second coat I run a curved 16" trowel through the middle, then skim it on the third. Once I. A while after I sand, if it's a bad one I'll double up with a curved trowel on either side again. Not much sanding in between coats- you dont want to take off what your trying to build out